The present invention relates to an antenna device mainly used for a radio machine for mobile communication such as a portable telephone.
Recently, demand for a radio machine for mobile communication such as a portable telephone has sharply increased. Service of text information or the like has been added to functions of the radio machine and variety of the functions has been increased. For responding to the variety, improved performance has been required for the radio machine. This market situation requires antenna device installed in the radio machine to be lightened and have higher sensitivity and a wider band.
An antenna device installed in a conventional radio machine is described hereinafter with reference to FIG. 22.
FIG. 22 is a perspective view illustrating a conventional antenna device and a mounting part with which this antenna device is mounted to a radio machine.
As shown in FIG. 22, conventional antenna device 5 comprises the following elements:
fitting metal 1 for attaching the antenna device to a radio machine body;
core part 2 fixed over fitting metal 1;
antenna element 3 placed on the outer periphery of core part 2; and
top cover 4 made of insulating resin for covering core 2 and antenna element 3.
Fitting metal 1 is made of metal and includes screw part 1A and recessed part 1B. Core part 2 is made of insulating resin such as acrylonitrile-butadiene-styrene (ABS). Antenna element 3 comprises winding part 3A formed by spirally winding a copper wire or a copper alloy wire on the outer periphery of core part 2, and antenna element""s lower part 3B under winding part 3A. Antenna element""s lower part 3B is fixed to the outer periphery of recessed part 1B of fitting metal 1. In this structure, antenna element 3 and fitting metal 1 are electrically connected.
Top cover 4 is made of insulating resin in order to cover core part 2 and antenna element 3.
Radio machine 6 has a tubular part for receiving antenna device 5 in its upper part, and metallic female screw 7 is fixed to the inside of the tubular part.
Connection terminal 8 is electrically connected to the metallic female screw 7. An end of connection terminal 8 is electrically connected to a prescribed circuit part over a wiring board (not shown in FIG. 22) placed in radio machine 6.
Conventional antenna device 5 is mechanically and electrically mounted to radio machine 6 by fastening screw part 1A of fitting metal 1 into metallic female screw 7.
When a given radio wave goes into antenna element 3, antenna element 3 induces high frequency current corresponding to the radio wave. The high frequency current induced by antenna element 3 flows to the prescribed circuit part placed in radio machine 6 through fitting metal 1, metallic female screw 7, and connection terminal 8. Thus, radio machine 6 can receive information carried by the radio wave. Radio machine 6 generates high frequency current corresponding to information to be transmitted in the prescribed circuit part, and transmits the generated high frequency current as radio wave through antenna element 3.
Conventional antenna device 5 has a structure where electric connection is obtained by fastening fitting metal 1 into female screw 7 of radio machine 6. Therefore, fitting metal 1 of antenna device 5 and female screw 7 of radio machine 6 must be made of metal. As a result, masses of antenna device 5 and radio machine 6 inconveniently increase.
In addition, in the conventional structure, the high frequency current induced at antenna element 3 of antenna device 5 flows to the prescribed circuit part placed in radio machine 6 through fitting metal 1, female screw 7, and connection terminal 8 in a state where antenna device 5 is mounted to radio machine 6. This structure includes many connections for guiding the high frequency current to the prescribed circuit. Electrical loss of the high frequency current is apt to occur at the connections, and may affect receiving sensitivity of radio machine 6.
The object of the present invention is to solve the conventional problems discussed above, and to provide an antenna device that is light, has less electrical loss of induced high frequency current, and can be easily and strongly mounted to a radio machine.
For attaining the object, the antenna device in accordance with the present invention comprises the following elements:
(a) an attachment part, made of insulating resin, attached to the radio machine;
(b) an antenna element, made of conductor, placed over the attachment part;
(c) a connection terminal formed at the attachment part for electrically connecting the antenna element to a circuit part of the radio machine;
(d) a snap part projecting from the attachment part; and
(e) a top cover, made of insulating resin, for covering the antenna element.
The snap part is constituted by a claw-shaped metal or a resin embedded with metal. The connection terminal for electrically connecting the antenna element to the circuit part of the radio machine is formed at the attachment part.
In this structure, connection terminal electrically connected to the antenna element directly connects to a prescribed circuit of the radio machine. Therefore, the antenna element and the prescribed circuit of the radio machine are electrically interconnected through the connection terminal. As a result, the attachment part can be made of insulating resin, and therefore, mass of the antenna device in the structure can be reduced. In addition, the structure can reduce connecting part where the electrical loss of the high frequency current is apt to occur, and thus, the structure hardly affect receiving sensitivity of the radio machine. Since a snap part having a metal part as a mounting means to the radio machine is formed at the attachment part, easy and strong mounting to the radio machine is allowed.
Since the snap part includes the metal part, it hardly bends or folds and can be strong.
When the metal part of the snap part and the connection terminal are integrally formed of one member in the antenna device of the present invention, number of components can be reduced, and positions of the metal part of the snap part and the connection terminal can be easily arranged in high accuracy. Therefore, the antenna device having good mountability to the radio machine and stable electric connectability can be easily provided.